Complex Phase Lag Behaviors of the 0.5 - 10 Hz QPOs in GRS 1915+105

Recent results on the inner disk oscillations found in GRS 1915+105 are reviewed. QPOs during the low state are used as a marker for such oscillations and the physical picture emerging from a combined X-ray spectral and timing analysis is examined. The relationship between inner disk oscillations and synchrotron radio emission is critically evaluated.

For all 209 RXTE observations of the X-ray nova XTE J1550-564 during its major outburst of 1998-1999, we have analyzed the X-ray power spectra, phase lags, and coherence functions. The phase lags and coherence measures are used to distinguish three types of low-frequency QPOs (one more than those reported by Wijnands, Homan, & van der Klis 1999). For the most common type, the phase lag is correlated with both the QPO frequency and the amplitude. The physical significance of t...

GRS 1915+105 can show type-C quasi-periodic oscillations (QPOs) in the power density spectrum. A high-frequency QPO (HFQPO) at 67 Hz has been observed in this source, albeit less often than the type-C QPOs. Besides these features, GRS 1915+105 sometimes shows a broad bump in the power spectrum at around 30-150 Hz. We study the power spectra of GRS 1915+105 with the Rossi X-ray Timing Explorer when the source was in the $\chi$ class. We find that the rms amplitude of the bump ...

Utilizing NICER observations, we present an analysis of the soft X-ray re-brightening event of GRS 1915+105 observed in 2021. During this event, we observed the emergence of a stable, long-lasting low-frequency quasi-periodic oscillation (LFQPO) with frequencies ranging from 0.17 to 0.21 Hz. Through a careful spectral analysis, we demonstrate that a low-temperature Compton-thick gas model well characterizes the emitted radiation. By examining the spectrum and identifying nume...

We present results of our analysis of a set of RXTE/PCA observations of X-ray flares/bursts with burst cycle ranging from 30 to 1300 s from the Galactic X-ray transient source GRS 1915+105 during last four years. These flares/bursts can be classified into four types: 1) regular bursts with short burst phase of about 20 s (R1), 2) regular bursts with short quiescent phase of about 20 s (R2), 3) long regular bursts (R3) with burst cycle > 1000 s, and 4) irregular bursts (IR). F...

We present a detailed study of the 5 Hz quasi-periodic oscillation (QPO) recently discovered in the bright X-ray transient and black-hole candidate GRS 1739-278 (Borozdin & Trudolyubov 2000) during a Rossi X-ray Timing Explorer observation taken on 1996 March 31. In total 6.6 ksec of on-source data were obtained, divided in two data sets of 3.4 and 3.2 ksec which were separated by 2.6 ksec. The 5 Hz QPO was only present during the second data set. The QPO increased in strengt...

The two galactic `microquasars' with superluminal radio jets have been quite active during 1996, generatinga variety of studies involving both NASA and ground-based observatories. GRS~1915+105 has displayed dramatic accretion instability in observations with RXTE, revealing X-ray light curves and emission states unlike anything previously seen. Variable QPOs in the range of 0.07--10 Hz have been monitored with the capability to track the individual oscillations. The QPO ampli...

We report a comprehensive study on spectral and timing properties of hard X-ray dips uniquely observed in some so-called variability classes of the micro-quasars GRS 1915+105 and IGR J17091-3624. These dips are characterized by a sudden decline in the 2.0-60.0 keV X-ray intensity by a factor of 4-12 simultaneous with the increase in hardness ratio by a factor of 2-4. Using 31 observations of GRS 1915+105 with RXTE/PCA, we show that different behavior are observed in different...

The active galactic nucleus (AGN) RE J1034+396 displays the most significant X-ray Quasi-Periodic Oscillation (QPO) detected so far. We perform a detailed spectral-timing analysis of our recent simultaneous XMM-Newton, NuSTAR and Swift observations. We present the energy dependence of the QPO's frequency, rms, coherence and phase lag, and model them together with the time-averaged spectra. Our study shows that four components are required to fit all the spectra. These compone...

The phase lag structure between the hard and soft X-ray photons observed in GRS 1915+105 and XTE J1550+564 has been said to be ``complex'' because the phase of the Quasi-Periodic Oscillation fundamental Fourier mode changes with time and because the even and odd harmonics signs behave differentely. From simultaneous X-ray and radio observations this seems to be related to the presence of a jet (level of radio emission). We propose a simple idea where a partial absorption of...